The present invention relates to a method of improving the productivity of a ruminant or ruminant-like animal and more particularly to a method of improving the productivity of ruminant or ruminant-like animals utilising an immunogenic preparation.
It is well known that micro-organisms in the rumen play a major role in determining the availability of nutrients to an animal. Under certain nutritional conditions the activities of some of the micro-organisms in the rumen including protozoa can seriously reduce the productivity of the animal to be significantly less than its potential.
Experimentally, it has been shown that in certain situations, removal of the protozoa from the rumen, or at least decreasing the activities of protozoa in the rumen, can result in an improvement in the ratio of protein to energy of the nutrients available for absorption from the gastro-intestinal tract of a ruminant animal. The improved nutrient availability results in an improvement in the productivity of the animal which can be measured in a variety of ways such as liveweight gain, improved milk production, improved efficiency of utilisation of feed and improved wool growth (sheep).
The present invention is based on the use of certain immunogenic preparations which have been found to be effective in altering the activities of rumen protozoa. Throughout the specification the term xe2x80x9cruminant animalsxe2x80x9d should be understood to include xe2x80x9cruminant-like animalsxe2x80x9d. Furthermore, where reference is made to a xe2x80x9crumenxe2x80x9d it will be understood that the term is being used so as to include the paunch of an animal classified as a ruminant-like animal.
Thus, the present invention provides a method of improving the productivity of a ruminant animal, the method comprising administering to said animal an amount of an immunogenic preparation effective to invoke an immune response to at least one rumen protozoan, the immune response invoked being effective in reducing and preferably totally removing the activity of the at least one rumen protozoan.
The immunogenic preparation employed in the method may be of various forms provided it invokes the appropriate immune response in the recipient. Preferably, the immunogenic preparation comprises an antigen preparation such as a vaccine comprising at least one antigen effective in invoking an immune response to at least one rumen protozoan. In this preferred form, the antigen preparation preferably comprises an antigen prepared from a washed preparation of at least one rumen protozoan and even more preferably the antigen preparation comprises a mixture of antigens, the antigens preferably being from a plurality of different species of rumen protozoa.
The rumen protozoa include a range of protozoa. However, preferably the at least one rumen protozoan is a member of the order Prostomatida, Trichostomatida or Entodiniomorphida. In one particularly preferred form, the at least one rumen protozoan is selected from the group of genera comprising; Diploplastron, Eodinium, Polyplastron, Entodinium, Dasytrichia and Isotrichia.
The rumen protozoa outlined above may be isolated from whole rumen contents by centrifugal elutriation. Preferably, and in the case of a sheep or another similar sized animal, the rumen protozoa have an approximate cell size between 10 and 100 xcexcm measured as diameter of a sphere of the same volume as the cell. In the case of rumen protozoa isolated from larger animals such as cattle the approximate size of the cells may be larger than the range outlined above. Thus, in a preferred form the immunogenic preparation used in the method of the present invention may comprise antigens obtained from rumen protozoa having an approximate cell size between 10 and 100 xcexcm. Alternatively the rumen protozoa may have an approximate cells size of between 5 and 200 xcexcm.
Additionally, or alternatively, the immunogenic preparation may comprise an immunogenic fraction(s), polypeptide(s)/peptide(s), polysaccharide(s), or lipopolysaccaride(s) derived from one or more rumen protozoa.
The immunogenic preparation may further comprise one or more adjuvants. The one or more adjuvants may be of various forms provided they act to improve the immune response invoked in the recipient. Preferably, the adjuvant comprises a DEAE-dextran based adjuvant and in one particularly preferred form the adjuvant comprises DEAE-dextran chloride. Alternatively, the adjuvant may be selected from the group comprising; Freund""s complete adjuvant (FCA), Freund""s incomplete adjuvant (FIA) and alum.
The ratio of the components of the immunogenic preparation may be varied according to preference and the mode of use to which the preparation is being put. For example, an immunogenic preparation for use on weaner wethers may comprise 20 mL of the antigen preparation (106 protozoa/mL), 20 mL of 20% (w/v in PBS) diethylaminoethyl (DEAE)xe2x80x94dextran chloride, 1 mL of 30% (v/v in PBS) glycerol, 1 mL of 1% (v/v in PBS) Tween 80 and 35 mL squalene. When using an immunogenic preparation of this form on weaner wethers a dose of 5 mL per animal has been found to be effective.
The method of the invention makes it possible for animals to have an improved productivity. In this respect, and as will be illustrated by the examples below, animals to which the method is applied show improved characteristics such as greater liveweight, liveweight gain, improved milk production, improved efficiency of gain and improved wool growth (for sheep). These aspects of improved productivity are improvements over the normal characteristics of those animals when not subjected to the method of the invention.
It is believed that the method of invention makes it possible to increase the ratio of protein to energy available for the animal for absorption in the gastro-intestinal tract by controlling rumen protozoa. It is envisaged that the control of the rumen protozoa occurs via a reduction in the number of rumen protozoa, and/or a reduction in the activity of rumen protozoa.
As protozoa are naturally present in the rumen of the vast majority of ruminant animals, it will be appreciated that animals exposed to the invention are thus considered healthy animals and actually represent the normal population of any given animal species.
Thus, otherwise healthy animals are able to be subjected to a method of the invention so that they have an improved productivity from a more efficient utilisation of ingested nutrients and/or enhanced intake of feed. For example, animals subjected to the method of the invention may be able to meet their normal dietary requirements from a reduced amount of food or from a food supply of reduced quality.
It is also believed that by modifying the activity of the rumen protozoa there is also an indirect effect on the activity of other micro-organisms in the rumen such as methane producing bacteria. In this respect, it is noted that some methane producing bacteria in the rumen appear to have a commensal relationship with the rumen protozoa. As such by modifying the activity of the rumen protozoa there may also be a corresponding effect on the production of methane.
It is envisaged that an immunogenic preparation such as a vaccine incorporating antigens from both methanogenic bacteria, in particular those classified as archae, and protozoa may be particularly effective in achieving the method of the present invention. Thus, the immunogenic preparation of the present invention may further comprise at least one antigen from at least one methanogenic bacterium. Preferably, the methanogenic bacterium comprise bacteria, classified as archae, from the rumen. Indeed, it will be appreciated that methanogenic bacteria are present in the rumen and some may be closely associated with the rumen protozoa. Thus, when the immunogenic preparation of the present invention is prepared from whole rumen contents (incorporating methanogenic bacteria) the improved productivity of the animal subjected to the method of the invention may be enhanced when an immune response is elicited against both the methanogenic rumen bacteria and the rumen protozoa.
The present invention will now be described by way of example in relation to the following examples. The examples illustrate various aspects of the present invention, but are in no way intended to limit the scope of the preceding description. In Examples 1 and 2 FIGS. 1C, 1D and 1F illustrate results after statistical analysis to remove data having a studentized residual of greater than three (ie approximately more than three standard deviations from the mean).